Synchronizing impulse generator for interlaced scanning



March 4, 1941. F. BELOW SYNCHRONIZING IMPULSE GENERATOR FOR INTERLACED SCANNING M Fil ed March 4, 1938 J1 T Z 6250 J1 3 T 7250 2239.2 w

\I! 1T If U 5\ 50 50 laced ratio of 2:1. According to Fig. 2, a master:

Patented 4, 19 41 I SYNCHRONIZING IMPULSE GENERATOR FOR INTERLACED SCANNING Fritz Below, Berlin-Klein Maclmow, Germany, asaignor to the iirm of Fernseh Aktiengesellschaft, Zehlendorf, near Berlin, Germany Application March 4, 1938, Serial No. 193,998

InG

ermany March 6, 1937 7 Claims. I (Cl. 178-695) It is: known-1n the art to transmit two series of impulses for-synchronization of interlaced television transmissions, one of whichseries of impulses contains the frame synchronizing impulses, while the other contains the line synchronizing impulses, which generally are a nonintegral multiple of the frame synchronizing impulses. Hence, the leading edge of the frame synchronizing impulses does not always coincide with the leading edge of the line synchronizing impulses. For an interlaced ratio of 2:1, this is the case only for altematlng frames.

The impulse series for one frame may possess the shape shown in Fig. 1a, while Fig. 1b shows the impulse'series for the subsequent frame.

Fig. 2 is a diagrammatic showing of the apparatus of my invention.

Figs. 3a, 3b, and 3c illustrate wave form's of the impulse generators. V

In such a series of impulses the problem arises of controlling the scanning generators for frame scanning by frame synchronizing impulses without interference from line synchonizing im- It has been proposed to double the numwith mechanical timers by, for instance, covering the apertures of a synchronizing disc at the correct sp t. In electrical impulse generators, however, such a suppression of the line synchronizing impulses preceding the frame synchronizing impulses is not known.

It is the object of the invention to produce a blanking impulse by means of an auxiliary generator, whereby the occurrence of the blanking impulse precedes the occurrence of the frame synchronizing impulse delivered by the main generator by between 2% to 5% of a frame period. This blanking impulse is used to suppress approximately 5-16 lines immediately before the occurrence of the frame synchronizing impulse. Simultaneously, the time synchronizing impulses can also be suppressed during the interval of the picture synchronizing impulse.

The drawing shows an embodiment of the invention for transmission of 375 lines at an interoscillator O is provided with a constant frequency frame impulses.

of 18,750 cycles. From this master oscillator an impulse series of- 50 square-topped impulses. per second is derived by means-of impulse generators, or frequency dividers I, 2, 3 and '4. The frequencies of the individual dividers are indicated in the drawing. The auxiliary generator 5 produces a series of impulses shown in Fig. 3a, the individual impulses of which have a duration of approximately 2% to 5% of the interval between I The auxil'iarygenerator 5 controls two impulse generators of 50 cycles, viz., a main generator 6, which is synchronized by the lagging edge of the impulse of the auxiliary generator 5 (Fig. 3b), and a blanking impulse generator 1, which is synchronized with the leading edge of the impulse produced by the auxiliary generator (Fig. 3c). Both generators 6 and 1 may be similar multi-vibratorswhich both respond to impulses of negative polarity. In this case, an impulse is applied to; generator 6 which has the opposite polarity of that shown in Fig.

. 311'. Main generator 6 may also be so constructed that it responds to an impulse of positive polarity. The duration of the impulse produced by main generator 6 is approximately 5% to 10% of the interval between frame impulses, while the impulse generated by the auxiliary generator has a duration of about 2% to 5% of this interval. In this manner itis accomplished that the impulse produced by each blanking generator occurs 2% to 5% earlier than the impulse of the main generator. The series of impulses produced by the blanking generator is used to key a line synchronizing impulse generator 8 which is controlled by the master generator I through a divider 9. As the blanking impulse always occurs approximately 2% to 5%, or 5 to 10 lines, prior to the frame synchronizing impulse, 5 to 10 line synchronizing impulses are suppressed immediately before occurrence of the frame synchronizing impulse, and the frame scanning generator is accurately synchronized with the leading edge of the frame synchronizing impulse undisturbed by line synchronizing impulses.

Multi-vibrators can be used as impulse generators; it may be understood, however, that they as well as the frequency dividers may consist of Thyratron-Kipp devices, vacuum tube Kipp circuits and other suitable circuits.

Having thus described my invention, I claim:

1. Method of generation of synchronizing impulses for interlaced television transmissions, having the characteristics that a series of squaretopped impulses of frame frequency control an,

' impulses have a duration of approximately 2% to 5% of the frame scanning period.

5. Method according to claim 1, having the characteristics that the impulse generators controlled by the leading and lagging edges of the impulse are of similar design and are controlled by impulses of opposite polarities.

6. Method according to claim 1, having the characteristics that the impulse generator controlled by the leading edge or the impulse responds to a voltage variation in one direction, while the impulse generator controlled by the lagging edge of the impulse responds to a voltage variation in the opposite direction.

7. Th method of synchronizing in the transmission of pictures or the like comprising generating line synchronizing impulses, generating frame synchronizing impulses, developing control impulses, blanking said line synchronizing impulses at the start of said control impulses and for a period equal to the duration of said control impulses, and controlling the generation of frame synchronizing impulses at the termination of said control impulses.

FRITZ BELOW. 20 

